The present invention relates to an injection device, particularly for medical use, such as syringes, particularly provided with a safety system aimed at protecting the injection needle after use.
In this application, the distal end of a component or of a device means the end furthest away from the hand of the user and the proximal end means the end closest to the hand of the user. Similarly, in this application, the terms “in the distal direction” and “distally” mean in the direction of the injection, and the terms “in the proximal direction” and “proximally” mean in the direction opposite to the direction of injection.
Injection devices, such as syringes, are well known. These injection devices are usually provided at their distal end with an injection needle that is designed to be inserted into the skin of a patient, and through which the product to be injected passes to the injection site. Normally, these syringes are provided with a piston rod whose distal end comprises a piston which, during the injection phase and under the action of a distal pressure exerted by the user on the piston rod, pushes the product through the injection needle.
One of the constant problems presented by the injection devices is the risk of accidental pricks likely to occur after the injection
In order to minimize these risks, it is known practice to furnish the syringes with means of protecting the needle after injection: these protection means may for example be in the form of a sleeve sliding relative to the syringe and required to cover the needle after the injection and the withdrawal of the needle from the injection site.
Certain of these protection means must be activated manually, the sleeve having to be moved manually by the end-user to cover the needle. Consequently, these protection means are not very reliable and not very practical to use. To remedy these disadvantages, injection devices have been designed with protection means that are automatically activated, for example by the movement of the piston rod which, when it reaches a predetermined position, releases the sleeve then deployed without additional manual intervention, by elastic means, for example a spring forcing its distal movement at the end of injection.
However, it happens that the automatic protection means are activated while the needle is still in the skin of the patient. In such a case, the sleeve begins to deploy and is then stopped by the skin of the patient against which it is pressed by the spring. The spring can therefore not deploy further in the distal direction and tends to deploy in the proximal direction, which causes the piston rod, and hence the piston, to rise again in the proximal direction into the body of the injection device. In other cases as described hereinafter, the piston rod is caused to rise again by the means for activating the protection means returning elastically to their initial position.
The user may then be confronted with a problem of reabsorption of the injected product due to the return movement of the piston rod, and hence of the piston, in the proximal direction. This return movement is usually limited in distance: however, it is sufficient to cause a portion of the product previously injected into the body of the patient to return into the body of the syringe, thereby causing an incorrect dosage of the injected product. The recommended dose of product is not injected in its totality and serious consequences for the patient may result therefrom.
Thus, there is the need for an injection device comprising automatic means of protecting the needle making it possible to prevent the phenomenon of the return of the piston in the proximal direction after injection, in particular when the injection needle remains at least for a moment in the skin of the patient after the end of the injection and when the automatic protection means are activated before it is withdrawn.
Publication WO 03/068298 A1 describes an injection device provided with automatic protection means activated by the piston rod when the latter arrives at the end of travel towards the end of the dose. The protection means comprise a sleeve held in a sheath by elastically flexible lateral lugs designed to be deflected by the head of the piston rod when the latter arrives at the end of travel. The spring provided for deploying the sleeve is placed between the sheath and the sleeve itself. Thus, if, at the end of injection, while the needle is still in the injection site, the user stops pressing on the piston rod, the spring will only have the effect of pressing the sleeve towards the skin of the patient without causing the piston rod to rise again. Nevertheless, this injection device has the major disadvantage of not allowing the moment when the protection means are activated to be controlled. It is therefore difficult, even impossible, to perform the injection of the end of the dose followed by the activation of the protection means. Either the activation might take place before the end of the dose is injected, and then the sleeve is released and pressed against the skin when the whole dose of product has not yet been injected, or the end of the dose might be injected without activation. Indeed, it is very difficult to reach a control level of the industrial process allowing the required accuracy of the dimensions and tolerances. Furthermore, the sheath of this injection device comprises elastically flexible intermediate lugs placed between the lateral lugs and the head of the piston rod. When the automatic protection means are triggered, if the user relaxes the pressure of the piston rod, the intermediate lugs return to their undeflected position causing the piston to rise again, hence a risk of reabsorption of the previously injected product.
There is therefore also the need for such an injection device making it possible to trigger the activation of the protection means at the moment desired by the user and to ensure that the end of the dose of product is injected without reabsorption.
Specifically, one of the problems encountered with the automatic protection means is the risk of activating them prematurely or inadvertently, during their use, even during the manufacture and/or assembly of the injection devices. Another associated risk is that of, after activation of the protection means, no longer being able to inject the end of the dose. Also, to alleviate these problems, the injection devices must be manufactured with extremely tight production tolerances aimed at the end of the dose coinciding with the activation of the activation means. These production tolerances are difficult to guarantee; the industrial processes for manufacturing the injection devices are thereby complicated and slowed and the injection device is more costly.
Publication WO 2005/030301 A1 describes an injection device provided with automatic protection means activated by the piston rod when the latter arrives at the end of travel towards the end of the dose. The automatic protection means comprise a sleeve designed to be deployed by a spring. Before activation, this sleeve is kept in the withdrawn position by immobilization means. This injection device also comprises means of retaining the sleeve. These retention means make it possible to prevent the deployment of the sleeve after activation of the immobilization means. The retention means are released by simply relaxing the distal pressure applied to the piston rod to allow the deployment of the sleeve. This injection device nevertheless does not make it possible to remove the risk of reabsorption when the user relaxes the pressure on the piston rod before withdrawing the injection needle from the injection site.
There is therefore the need for an injection device that prevents the return of the piston after injection and that is provided with needle protection means that can be activated automatically but only when the end-user so decides, making it possible, after activation of the protection means, to allow the injection of the end of the dose, and that is easy to manufacture.
Moreover, such an injection device must be of simple use for the user. In this view, it must appear as reassuring for the user and must not present any features capable of instilling doubt in the user's mind that the device is not safe or not working.
The object of the invention is therefore to provide an injection device, particularly a syringe, of simple and reassuring use for the user, provided with needle protection means activated automatically at the end of injection, the activation of the needle protection means being controlled by the user, which prevents inadvertently activation of the automatic protection, thus providing perfect safety against the risks of accidental pricks, and which also prevents the return of the piston after injection. Another object of the invention is to propose such an injection device with needle protection means making it possible to inject the end of the dose and capable of being easily manufactured industrially.